The longterm aims of this project are to understand the molecular mechanisms of agonist recognition and G protein coupling of peptide receptors, and to elucidate the mechanisms of peptide receptor desensitization. The pituitary adenylate cyclase activating peptide (PACAP) is a recently discovered 38 amino acid neuropeptide identified in hypothalamic extracts by its ability to potently and powerfully activate adenylate cyclase activity in cultured pituitary cells. PACAP also exist as a 1-27 amino acid cleavage product (PACAP-27). Amino acid sequence analysis indicates that PACAP-27 is highly homologous to vasoactive intestinal peptide (VIP), one of the most important peptide mediators of coronary, cerebral, and peripheral arterial vasodilation. VIP is a member of the glucagon/secretin family of neuropeptides, and by homology PACAP joins this family. Two PACAP receptors, classified as Types I and II, are present in CNS and peripheral tissues, respectively. Type II receptors also appear to bind to VIP with high affinity. The VIP and secretin receptor cDNA's have recently been cloned, but little homology is present. These data and others suggest that the PACAP and VIP receptors may be a new sub-family of G protein coupled receptors. The cloning of the cDNA of the PACAP receptor or receptors will greatly enhance the understandings of the VIP/PACAP receptor subfamily. Therefore, the specific aims of the present application include: (1) molecular cloning of the cDNA which encodes the pituitary adenylate cyclase activating peptide (PACAP) receptor; (2) molecular and pharmacologic characterization of the PACAP receptor cDNA; and (3) evaluation of the agonist binding and G protein coupling relationships of the VIP and PACAP receptors. An expression cloning approach with COS cells will be used to isolate the PACAP receptor cDNA. Complete pharmacologic evaluation will follow, including an evaluation of the receptor for regions important for agonist and G protein binding.